1. Field of the Invention
The present invention relates to an electronic device which uses a detachable battery pack as its power supply, such as a portable radio communication apparatus, a battery pack, a charger for the battery pack and their peripheral devices.
2. Description of the Related Art
A portable radio communication apparatus uses a detachable battery pack as a power supply. Plural types of battery packs are available for such a portable radio communication apparatus in view of the portability and power-supply efficiency of the equipment. Each battery pack incorporates one of several different specifications of batteries (voltage or current capacities). The batteries include a nickel-cadmium battery, an alkaline battery, and a manganese battery. Generally, the nickel-cadmium battery which is rechargeable is used.
Portable radio communication apparatus has several usage modes, a standard usage mode, prolonged usage mode, high-power usage mode and prolonged high-power usage mode. A battery pack for the standard use incorporates a standard battery, a battery pack for the prolonged use incorporates a battery which has a large capacity, a battery pack for the high-power use incorporates a battery which outputs a high voltage, and a battery pack for prolonged high-power use incorporates a battery which has a large capacity and outputs a high voltage.
A portable radio communication apparatus which uses a battery pack has a function of automatically discriminating the type of the battery incorporated in the installed battery pack and switching the operation mode (operation parameter) to the one that matches with the battery type.
When the battery in the battery pack is a rechargeable type, it is necessary to select a charging power supply appropriate for the battery type to charge the rechargeable battery. A conventional charger for battery packs therefore has a plurality of charging power supply circuits, automatically discriminates the type of installed battery pack and selects the charging power supply circuit that matches with the battery pack to charge the incorporated battery.
FIG. 6 shows the structures of a portable radio communication apparatus, battery packs and a charger for the battery packs, according to the prior art.
In FIG. 6, battery packs 121, 122 and 123 respectively incorporate rechargeable batteries A1, A2 and A3 of different specifications (rated: current capacities/output voltages/charging voltages), and each has output terminals TB1, TB2, TB3 and TC and charging input terminals TD1, TD2, TD3 and TE.
The positive electrode of the battery A1 in the first battery pack 121 is connected to the terminals TB1 and TD1. The positive electrode of the battery A2 in the second battery pack 122 is connected to the terminals TB2 and TD2. The positive electrode of the battery A3 in the third battery pack 123 is connected to the terminals TB3 and TD3. The negative electrodes of the batteries A1 to A3 in the battery packs 121 to 123 are all connected to the terminals TC and TE.
A communication apparatus body 11 has power supply terminals TF1, TF2, TF3 and TG, which are respectively connected to the terminals TB1, TB2, TB3 and TC of each of the battery packs 121 to 123.
A terminal voltage detector 113 detects which terminal, TF1, TF2 or TF3, is connected to the battery in the battery pack 121, 122 or 123 from the voltage levels at the terminals TF1, TF2 and TF3, and discriminates the connected battery pack (its specification). In accordance with the discrimination of the terminal voltage detector 113, an operation mode switching controller 114 switches the operation mode of a communication circuit 112 to the mode associated with the installed battery pack.
A charger 13 has terminals TH1, TH2, TH3 and TI, which are connected to the terminals TD1, TD2, TD3 and TE of any of the battery packs 121-123, and includes a charging power supply circuit 131 for outputting charge voltages to the power supply terminals TH1, TH2 and TH3 to charge the batteries A1, A2 and A3 respectively.
When the battery pack 121, 122 or 123 is attached to the charger 13, the incorporated battery A1, A2 or A3 is charged with the voltage appropriate for this battery, through the terminal TD1, TD2 or TD3 connected to the battery.
According to the structure shown in FIG. 6, as the types of battery packs increase, the number of terminals provided on the communication apparatus body 11, the battery packs 121-123 and the charger 13 should also be increased. That is, as the types of battery packs increase, the number of terminals inevitably increases, which does not meet the demand on a portable electronic device for compactness and lighter weight.
U.S. Pat. No. 5,164,652 discloses a system which discriminates the type of an installed battery pack and can overcome this problem. The contents of this patent are incorporated herein by reference.
According to the technique disclosed in the patent, as shown in FIG. 7 of this application, when a battery (battery pack) 1 is attached to a battery driver (radio transceiver) 2, their associated power supply terminals 3, ground terminals 4 and detection terminals 5 are connected together. The detection terminal 5 of the battery driver 2 is connected via a resistor 6 to the supply voltage while the detection terminal 5 of the battery 1 is grounded via a resistor 7 whose resistance is specific to the battery type and differs from those of different types of batteries.
Therefore, the voltage at the detection terminal 5 changes in accordance with the type of the battery 1 attached to the battery driver 2. A battery-type detector 8 detects the voltage at the detection terminal 5, compares the detected value with a predetermined reference level (for discrimination of the battery type) to discriminate the type of the connected battery 1. A switch controller 9 switches the operation mode of a communication circuit based on the result of the discrimination by the battery-type detector 8.
According to the technique taught in the patent, the battery-type detector 8 provides the reference level for the discrimination of the battery type. If there are many types of batteries 1, therefore, it is necessary to alter the hardware of the battery-type detector 8.
When the voltage in the battery pack 1 becomes unstable (low), the voltage applied to the pull-up resistor 6 falls below the proper value, the voltage at the detection terminal 5 is not specifically determined in accordance with the type of the installed battery pack, so that the battery-type detector 8 may erroneously discriminate the type of the installed battery pack 1.
Further, the charger for charging the battery 1 having the structure shown in FIG. 7 cannot charge the batteries A1, A2 and A3 in the conventional battery packs 121, 122 and 123 shown in FIG. 6. Furthermore, the battery pack 1 with the structure shown in FIG. 7 cannot supply power to the communication apparatus body 11 shown in FIG. 6.